Deliberately impassive or expressionless.
Impassive.
Having such a face or look.
A style of comedic delivery in which something humorous is said or done while not exhibiting a change in emotion or facial expression.
In a deadpan manner.
To express (oneself) in an impassive or expressionless manner.
That cannot be investigated or searched into; unknowable, inscrutable.
Not capable of being searched; on which one cannot perform a search.
That cannot be sought out or looked for.